868
Anal. Chem. 1981, 53, 868-873
Cadmium(I1)-Exchanged Zeolite as a Solid Sorbent for the Preconcentration and Determination of Hydrogen Sulfide in Air Sivasankararao Vasireddy, Kenneth W. Street, Jr.,' and Harry
B. Mark,
Jr."
Department of Chemistty, Universiw of Cincinnati, Cincinnati, Ohio 4522 1
Hydrogen sulfide In air sorbs onto Zeolite AAA molecular sieves in the Cd(I1) (white) form to give CdS (yellow) in the concentration range required for the determination of H,S for personnel monitoring and excursion samples as well as highlevel (ppb) air samples. The immoblilzed sulfide Is determined by spectrophotometry after conversion to methylene blue wHh a spectrophotometric detection limit of 0.25 pg of sulfide. Linear calibration curves cover the range of 0.25-35 pg of H2S. Factors affecting collection characteristics of the solid sorbent such as breakthrough, humidity, storage time, and interference by other atmospheric constituents were studied. Actual monitoring data are presented.
One of the most commonly accepted methods for the determination of H2S in the air utilizes a liquid sorbent impinger containing a Cd(OH)2suspension ( 1 , 2 )which immobilizes S2in the form of CdS. Other metal salt solutions as well as solutions of caustic soda have been used as liquid sorbents for the entrapment and determination of this pollutant (3-9). In terms of personnel monitoring, liquid sorbents are cumbersome and somewhat restrictive, hence the recent emphasis in pollutant monitoring has been toward the use of solid sorbents for the preconcentration of gaseous air pollutants. A small tube containing 2 pg of collected S2-. Data in Table I should be used as a guide to the number of extractions necessary for each sample by comparing the color of the samples to the color of standard amounts of H2Scollected on Cd(I1)-exchanged zeolite. For samples requiring multiple
extractions there is no relationship between amounts recovered during each extraction, but the total recovered was found to be a constant (ca. 80%) for four-point calibration curves constructed on each day of sampling at these high levels, Linear calibration curves were obtained during every experiment. This will not be necessary in H2S analysis of most ambient air samples since it is normally present in
